DTMF decoder problem

• 03-14-2008, 09:15 PM
vallikranth
DTMF decoder problem
hi
I am making a cell phone controlled robot based on the DTMF tones. Iam using the HT9170B decoder. However Iam not getting the binary code o/p from the decoder. Here is the circuit Iam using

appliction circuit 1 of HT 9170B datasheet at
http://datasheet.digchip.com/196/196...-0-HT9170B.pdf
(I don't know how to post the pic of the ckt)

Now the problem I think is that the capacitor .1uF connected to pin 18 and resistor 300k connected to pin 16 do not provide adequate delay. Can anyone tell me what values of this capacitor and resistor must be used for a valid binary o/p??( if wrong correct me)
• 03-15-2008, 05:15 PM
allbits
What did you do to OE??

pin 10?? just go through the function of OE.
• 03-15-2008, 10:03 PM
vallikranth
hi allbits

I have connected the OE pin to 5v. Yea I have read the datasheet thorougly. As asked in my previous post I want to know whether the resistor and the capacitor values given in data sheet are correct since Iam not getting the o/p with that ckt. I think the RC time constant at o/p is not sufficient to check the valid signal duration condition.
• 03-16-2008, 07:53 AM
allbits
1) Check your input tone - the duration and the tone.
2) Check crystal freq.
3) Connect pins 5,6 to ground.
4) try using a 22K resistor and .1uf cap (again, depends on your input tone duration - mentioned in page 5, with equations)

are you taking the tone from the telephone lines or are you generating it??
• 03-16-2008, 12:52 PM
vallikranth
Iam taking the tone from telephone line.
1. How to check the tone and its duration??
2. Crystal frequency is ok
3. Already tried connecting those pins to gnd
4. Tried using 22k and .1uF also but in vain

I have replaced three ICs thinking that Ic may be faulty. Can you let me know how to check HT9170B. I have tested it using both analog and digital testers in my college but this IC is not recognised
• 03-16-2008, 03:25 PM
allbits
can you 'hear' the tone that is being send?? use an extension line.

what type of capacitor did you use in the input line?? it should have a higher voltage rating. use 400V. other than that, it should work well.

or, you can buy a 91214B and generate the tone, connect the tone o/p to the DTMF in and check the IC. If you have access to a CRO, see the tone waveform with the CRO. It is a beauty to watch.

but then, this is a robotics forum!!
• 03-22-2008, 08:47 PM
tpsbpl
• 04-13-2008, 10:23 PM
vallikranth
The circuit finally worked by making the following modifications

* Replacing 300k with 22k
* Grounding 5 and 6 pins
* giving the tone input directly to pin 3 but not as shown in the diagram